From GB 2193485A it is known to insert a stiffening sleeve in the plastic tube at the weld point to prevent deformation of the plastic tube during welding. U.S. Pat. No. 4,126,167 discloses the use of a nozzle arrangement with wedge-shaped parts instead of a plastic tube with a circular cross section, said wedge-shaped parts extending between the bag walls to prevent an abrupt transition between the plastic films and the nozzle arrangement. From EP 0269419 A1 it is known to arrange a nozzle on the outer face of the plastic tube and the plastic films to ensure a liquid-tight seal between the tube and the bag.
DE 19752648 C1 discloses pre-heating of the plastic tube before it is welded together with the plastic films to improve the weld in the critical transition areas.
From EP 0491380 A2 it is known to arrange shaped pieces of a heat-conducting material around the plastic tube and the plastic films during the welding process and to remove the shaped pieces from the plastic tube and the plastic films only after the welded areas have cooled.